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The stress-strain relationship of visco-elastic materials, generally used in the damping treatment of structures, can be described by two properties, such as the perfectly elastic (in-phase) stress-strain modulus and the loss factor. The values of these properties need to be determined in tension or compression for materials used as unconstrained damping layers and as anti-vibration mountings under machinery and under foundation blocks. Using a dual channel FFT analyzer, the specimen can be excited using wide band random excitation, and the properties determined from the frequency response spectra, as a continuous function of frequency, as shown in the following. Another possibility is to preload the specimen by a well-known mass, such that the preloaded damping material becomes a part of a resonant mass-spring-damper system. Damping, e.g. loss factor, is then determined from the 3 dB bandwidth of the resonance.

A simple set-up for quick and purely electrical QC testing of knock sensors is described in this paper. The main goal is to measure the “impedance” frequency response function of the sensors. The advantages of the test procedure described in this paper are as follows: Simple “pseudo” one channel measurement, from the operator's point of view. Electrical testing, i.e. no need for shakers, power amplifiers, elaborate fixtures etc.. Pulse excitation, thus very fast - in the order of 100ms for one measurement test. No averaging needed. Standard frequency response function display is used, i.e. no complex postprocessing needed. The only requirement is a small junction box with the necessary transformer and some electronics. The power supply for the junction box is the analyzer. The testing method can be extended to other types of transducers such as accelerometers.